1. Field of the Invention
The present invention relates generally to a reverberation apparatus, and is directed more particularly to a reverberation apparatus in which the frequency band of a reverberation sound is expanded.
2. Description of the Prior Art
A reverberation apparatus, which is widely known in the art, will be explained with reference to the graph of FIG. 1. In the prior art reverberation apparatus, a constant voltage type (in which the ratio between input and output voltages, or a so-called voltage amplifying factor, is constant regardless of frequency) is generally used as a driving amplifier. An original is supplied through the driving amplifier to a converter of a moving magnet type, and a spring is driven by the vibration of a magnet in the converter.
However, the impedance of a coil provided in the converter is substantially j .omega. L (.omega. is the frequency of the original signal flowing through the coil and L is the inductance of the coil), and increases substantially in proportion to the frequency of the original signal as shown in the graph of FIG. 1.
Accordingly, in a high frequency band where the impedance of the coil increases, the current flowing through the coil is decreased. Since the driving force for the spring is in proportion to the current flowing through the coil if the other conditions are constant, the high frequency band characteristic of the reverberation sound provided by the prior art reverberation apparatus in which the constant voltage type driving amplifier is connected to the coil, is deteriorated.
To avoid this defect, in the prior art an arrangement is proposed in which a resistor having a high resistance value is located at the stage prior to the coil in the converter, and the output signal from the driving amplifier is supplied to the series circuit of the coil and the resistor. In this manner, the variation accompanied by the frequency of the current flowing through the coil can be reduced.
However, in order to make the current variation as small as possible, it is necessary to increase the resistance value of the resistor indefinitely. If the resistance value of the resistor is increased as set forth above, the current flowing through the coil is reduced, which results in the driving force for the spring being decreased.